Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR PRODUCING CORRUGATED CARDBOARD
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/936,411, filed June 20, 2007, the entire disclosure of
which is
hereby incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to the production of
corrugated cardboard, and more particularly, to a novel and improved method
for
accurately controlling the application of an adhesive to the flutes of
corrugated
board centered on the flute crests, so that the flutes can be bonded to a
face.
BACKGROUND OF THE INVENTION
[0003] Corrugated cardboard composite is used in a large number
of applications. It is particularly desirable in packaging applications
because it is
rugged and has high dimensional and structural integrity.
[0004] Typically, corrugated cardboard is formed by producing a
corrugated sheet which is initially bonded along one side to a single face.
Adhesive is then applied to the crests of the flutes remote from the single
face by
an applicator roll of a glue machine. Thereafter, a second face is applied to
the
adhesive on the flutes to produce a composite structure in which corrugations
extend between and are bonded to spaced-apart faces.
[0005] In some instances, multiple-layer cardboard is produced in
which more than one corrugated sheet is adhesively attached to additional
faces
so that, for example, a central flat face is bonded to a corrugated sheet on
each
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side thereof, and outer flat faces are bonded to the sides of the two
corrugated
sheets remote from the central face.
[0006] The corrugated sheet is typically passed between a web
positioning roll and an applicator roll to apply the adhesive to the flutes.
The web
positioning roll typically applies sufficient downward pressure to force the
flute
tips into contact with the applicator roll. This downward pressure causes
compression or deformation of the flutes. The flutes enter the adhesive layer
prior to being crushed against the applicator and often become overly wetted
or
saturated with adhesive due to the long dwell time. As a result, the flutes do
not
return to their original shape after being crushed. This permanent deformation
of
the flutes reduces the strength of the final cardboard.
[0007] To carry out this method, a conventional corrugator glue
machine has been used for applying glue to exposed flute crests opposite the
first-face sheet. However, the adhesive applied to the flutes can be
asymmetrical
because the flutes plow through the adhesive layer on the applicator and are
wetted on one sloped face more than the other. This asymmetrical application
of
the adhesive results in a lower bond strength for a given weight of adhesive
and
a rough surface finish on the face sheet due to warpage after the adhesive
cures.
Additionally, a relatively large amount of over spray is created which further
increases the amount of glue used by the process. In one solution, the glue
film
can be applied to the outer surface of the applicator as described in U.S.
Pat. No.
6,602,546, which is incorporated herein by reference.
[0008] Still, there is a need in the art for an improved method for
producing corrugated cardboard which obtains maximum strength in the finished
product and an improved surface finish on the face. Furthermore, it can be
desirable to apply substantially less adhesive per unit area of the finished
product
and to produce the improved cardboard at an increased rate of production. It
is
particularly desirable to provide a method of applying adhesive accurately and
sparingly to the centers or crests of the corrugated flutes without
significant
adhesive being applied to either the leading or trailing sloped faces of the
flutes.
Most preferably, such a method may employ a control system programmed to
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automatically adjust any or all of a pressure loading force to be applied to
the
corrugated flutes of various flute sizes, a gap width between the rollers,
relative
alignment of the rollers (i.e., parallelism), and/or even automatically detect
flute
height.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention provides a method and apparatus for
uniformly and accurately applying adhesive to the crests of the flutes of
corrugated sheets with little or no (or substantially no) adhesive being
applied to
either the leading or trailing sloped faces of the flutes. In accordance with
the
present invention, higher line speeds can be achieved, tighter performance
specifications exceeding the capability of the industries standard machines
are
possible, and a significant reduction in the amount of glue used is achieved.
In
addition, accurately centering the adhesive onto the crests of the flutes
provides
stronger bond strength between the corrugated sheet and the adhered-to face
sheet. Directional differences in strength are minimized or substantially
eliminated, and surface smoothness of the face sheets is improved
(washboarding reduced). Because the adhesive is very accurately deposited only
to the flute crests, it is possible to reduce the adhesive weight deposition
rate
about 10-70%, or even more, of that required in conventional machines while
delivering the same or comparable bond and crush strength. Additionally,
because there is no practical lower limit to the controlled glue weight, cold
set
adhesives can be used to further improve board properties and reduce energy
costs and warpage losses. Furthermore, in accordance with the present
invention, smoother and more printable boards with greatly reduced warpage and
improved surface finish are produced.
[0010] To achieve still further aspects and in accordance with the
present invention, a method of applying adhesive to flutes of a corrugated
sheet,
where each the flute has a crest, is provided. The method includes the steps
of
applying a layer of adhesive on an outer surface of an applicator roll and
rotating
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the applicator roll, and rotating a web positioning roll adjacent said
applicator roll.
The web positioning roll and said applicator roll each have a rotational axis
and
define a gap between respective outer surfaces thereof. The corrugated sheet
is
moved, via rotation of the web positioning roll, along a path adjacent the
outer
surface of the applicator roll to apply adhesive to the flutes from the layer
of
adhesive, and the path of the corrugated sheet proceeds through the gap. A
control system is utilized to automatically maintain each of the rotational
axes
substantially parallel to one another based upon a comparison of a plurality
of
measurements of the width of the gap, and the crest of the flute is contacted
with
the applicator roll thereby depositing glue on the crest.
[0011] To achieve still further aspects and in accordance with the
present invention, a method of applying adhesive to flutes of a corrugated
sheet,
where each the flute has a crest, is provided. The method includes the steps
of
applying a layer of adhesive on an outer surface of an applicator roll and
rotating
the applicator roll, and rotating a web positioning roll adjacent said
applicator roll.
The web positioning roll and said applicator roll define a gap between
respective
outer surfaces thereof. The corrugated sheet is moved, via rotation of the web
positioning roll, along a path adjacent the outer surface of the applicator
roll to
apply adhesive to the flutes from the layer of adhesive, and the path of the
corrugated sheet proceeds through the gap. An average height of a plurality of
the flute crests is measured, and a desired width of the gap is determined
based
upon the average height. A control system is utilized to automatically adjust
the
position of the web positioning roll relative to the applicator roll to
maintain the
desired width of the gap, and the crest of the flute is contacted with the
applicator
roll thereby depositing glue on the crest.
[0012] To achieve still further aspects and in accordance with the
present invention, a method of applying adhesive to flutes of a corrugated
sheet,
where each the flute has a crest, is provided. The method includes the steps
of
applying a layer of adhesive on an outer surface of an applicator roll and
rotating
the applicator roll, and rotating a web positioning roll adjacent said
applicator roll.
The web positioning roll and said applicator roll define a gap between
respective
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outer surfaces thereof. The corrugated sheet is moved, via rotation of the web
positioning roll, along a path adjacent the outer surface of the applicator
roll to
apply adhesive to the flutes from the layer of adhesive, and the path of the
corrugated sheet proceeds through the gap. An average height of a plurality of
the flute crests is measured, and a desired pressure to be applied to the
flute
crests passing through the gap is determined based upon the average height. A
control system is utilized to automatically adjust the position of the web
positioning roll relative to the applicator roll to maintain the desired
pressure, and
the crest of the flute is contacted with the applicator roll thereby
depositing glue
on the crest.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The foregoing and other aspects of the present invention will
become apparent to those skilled in the art to which the present invention
relates
upon reading the following description with reference to the accompanying
drawings, in which:
[0014] FIG. 1 shows a side view of a corrugator glue machine
according to an aspect of the invention;
[0015] FIG. 2 shows a top perspective view of the corrugator glue
machine of FIG. 1;
[0016] FIG. 3 is an enlarged fragmentary view, partially in cross-
section, showing a portion of the glue mechanism of FIG. 1 at an interface
between an applicator roll and a web positioning roll;
[0017] FIG. 4 is an enlarged view as in FIG. 3, showing glue being
applied to the flute crests of a corrugated sheet along a path between the
applicator roll and the web positioning roll according to another aspect of
the
invention;
[0018] FIG. 5 is a schematic view of an example drive system for
driving the applicator roll and for controlling the speed thereof;
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[0019] FIG. 6 is an enlarged elevation view of a single face
corrugated sheet of with adhesive applied to the crests of the flutes;
[0020] FIG. 7A is a top view showing parallel alignment between an
applicator roll and a web positioning roll;
[0021] FIG. 7B is similar to FIG. 7A, but shows a skewed alignment
between the applicator roll and the web positioning roll;
[0022] FIG. 8A is a flow-chart showing an example control algorithm
for use with a control system in accordance with another aspect of the present
invention;
[0023] FIG. 8B is a continuation of the flow-chart of FIG. 8A;
[0024] FIG. 9 is a schematic view of an example non-contact
automatic flute height measurement system in accordance with another aspect of
the invention; and
[0025] FIG. 10. is a schematic view of an example contact
automatic flute height measurement system in accordance with another aspect of
the invention.
DESCRIPTION OF EXAMPLE EMBODIMENTS
[0026] Example embodiments that incorporate one or more aspects
of the present invention are described an illustrated in the drawings. These
illustrated examples are not intended to be a limitation on the present
invention.
For example, one or more aspects of the present invention can be utilized in
other embodiments and even other types of devices.
[0027] As used herein, the terms 'glue' and 'adhesive' are used
interchangeably, and refer to the adhesive that is applied to the flute crests
of a
corrugated sheet according to the invention as hereinafter described. Also as
used herein, the term 'web' refers to the corrugated sheet traveling through a
glue machine 10, and particularly as it travels past an applicator roll for
applying
adhesive thereto as will be further described. In the description that
follows, and
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from the drawings, it will be apparent that the web speed can be controlled,
at
least in part, by the rotational speed of the web positioning roll.
[0028] Herein, all machine elements or members, such as support
arms 20a and 20b, cross member 25, etc., are considered to be rigid,
substantially inelastic elements or members under the forces encountered by
them in the described corrugator glue machine 10. All such elements or
members can be made using conventional materials in a conventional manner as
will be apparent to persons of ordinary skill in the art based on the present
disclosure.
[0029] A corrugator glue machine 10 for use with the present
invention is provided having an idler roller and a web positioning roller that
cooperate to at least partially define a serpentine web path through the
machine.
A position of the positioning roller is freely adjustable within a
predetermined
range during operation of the machine.
[0030] Turning to the shown example of FIG. 1, an example
embodiment of a corrugator glue machine 10 is shown, incorporating an example
web tension nulling mechanism such as described in U.S. Pat. No. 7,267,153,
which is incorporated herein by reference. Although not required for use with
the
present invention, the web tension nulling mechanism can be effective to
cancel
out forces exerted on the web positioning roller resulting from tension in the
web,
such that these forces do not substantially affect the position of the
positioning
roller within the predetermined range. It is to be understood that while not
required, use of such a web tension nulling mechanism as described herein can
be beneficial when used in cooperation with the method of the present
invention.
[0031] The glue machine 10 generally includes a delivery idler roller
12, a web positioning roller 14 and a glue applicator roller 16 substantially
similar
in placement as the corresponding rollers described above. In operation, the
web
is conveyed toward and around the delivery idler roller 12, then toward and
around the web positioning roller 14 in a generally serpentine path such that,
on
traversing a gap 18 defined between the rollers 14, 16, the web 5 is oriented
having its flutes 7 facing the glue applicator roller 16 and is pressed up
against
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the outer circumferential surface of that roller 16 to achieve the desired
level of
glue application onto the exposed flute crests 6 of the passing web 5.
[0032] The delivery idler roller 12 is rotationally attached to a first
support arm 20a whose proximal end is pivotally attached to a base 40 of the
glue machine 10 (or to rigidly connected members which together comprise a
base for the glue machine) at support pivot joint 22a. The web positioning
roller
14 is rotationally attached to a second support arm 20b, whose proximal end is
pivotally attached to the base 40 of the glue machine 10 at a second support
pivot joint 22b. Each of the support arms 20a and 20b is independently
pivotable
relative to the base 40 of the glue machine about its own respective support
pivot
axis defined at its respective pivot joint. In one example embodiment, each of
the
support pivot joints 22a and 22b can be located or vertically aligned
substantially
beneath the center of gravity (axis of rotation) of the respective roller 12,
14
during operation of the glue machine, so the roller masses do not induce
significant moments about the pivot joints in their respective support arms
20a,
20b which must be compensated for by a control system 70, which may include
the actuators 50 (described below). Alternatively, each of the support arms
20a
and 20b can be pivotally attached at its proximal end at the same pivot joint
(e.g.
on the same shaft) or at coaxially aligned pivot joints, so long as the
support
arms 20a and 20b remain independently pivotable relative to one another
(except
as a result of the cross member 25, described below).
[0033] A cross member 25 is provided extending transversely of,
and linking the first and second support arms 20a and 20b as described in this
paragraph. The cross member 25 is pivotally attached at its first end to the
first
support arm 20a at a first linking pivot joint 26, and at its second end to
the
second support arm 20b at a second linking pivot joint 27. Thus, the cross
member 25 is freely pivotable relative to each of the first and second support
arms 20a and 20b at the respective linking pivot joint 26, 27, and but for its
attachment to the other support arm at its opposite end, the cross member 25
would be free to rotate about each of the linking pivot joints at each support
arm.
The geometry of the cross member 25 is selected based on the locations of the
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rotational axes of the idler and positioning rollers 12 and 14 relative to
their
respective support pivot joints 22a and 22b so that the greater moment
generated at the idler roller 12, compared to that generated at the
positioning
roller 14, from web tension is mechanically balanced out to achieve
equilibrium in
both support arms based on web tension-induced forces. Thus, as described in
U.S. Pat. No. 7,267,153, which is incorporated herein by reference, the web
tension nulling mechanism, via the cross member 25, can be effective to cancel
out forces exerted on the web positioning roller resulting from tension in the
web,
such that these forces do not substantially affect the position of the
positioning
roller within the predetermined range.
[0034] It will be understood that FIG. 1 is a side view, and that
typically the glue machine 10 will have two "first" support arms 20a located
at
opposite ends of the laterally extending delivery idler roller 12, as well as
two
"second" support arms 20b located at opposite ends of the laterally extending
web positioning roller 14 (see FIG. 2). In the illustrated embodiment, each of
the
rollers 12 and 14 is rotationally supported on a respective axially extending
lateral shaft 31,32 that is supported at its opposite ends on the paired
"first"
support arms 20a or the paired "second" support arms 20b as shown in FIG. 2.
In
this embodiment, a suitable cross member 25 is provided linking both sets of
the
adjacent first and second support arms 20a and 20b located on either side of
the
glue machine 10, with each cross member 25 having suitable geometry as
described above to null out web tension effects. Alternatively, the glue
machine
can be provided such that each of the rollers 12 and 14 is rotationally
supported
on a shaft that is cantilevered from a single support arm, such as the
respective
first and second support arms 20a and 20b shown in FIG. 2, located on only one
side of the machine. In this case, a cross member 25 is provided on only one
side of the machine 10 linking the first and second support arms 20a and 20b.
[0035] The present invention has been described as optionally
incorporating a web tension nulling mechanism that is provided with respect to
a
transversely extending cross member 25 pivotally linked to first and second
support arms 20a and 20b, which in turn support the idler roller 12 and web
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positioning roller 14. However, the nulling mechanism is not to be
correspondingly limited to this construction. For example, it is possible and
contemplated that linkage systems comprising a plurality of members can be
incorporated to dynamically link the idler and positioning rollers 12 and 14,
or the
first and second support arms 20a and 20b, so as to effectively cancel out the
web tension-induced forces as described herein; the invention is not limited
to a
single cross member 25. Also, it will be evident to the person of ordinary
skill in
the art, on reading the present disclosure, that other mechanical linkages or
linkage systems can be established to achieve the web tension nulling effect
as
described, herein, so that the actuator 50 that is operatively coupled to the
positioning roller 14 is shielded from web tension-induced forces during
operation
of the glue machine 10. It is contemplated that the present invention can
include
all such mechanical linkages and linkage systems. The constructions disclosed
herein are provided to illustrate exemplary embodiments of the invention.
[0036] Using such a mechanism, it is possible to provide very
precise gap-width control at the nip 18 between the positioning and glue
applicator rollers 14 and 16. Consequently, the pressure at which the flutes 7
are
compressed against the roller 16 surface (and the corresponding degree of
compression of those flutes 7) can also be very precisely controlled. The glue
can be provided in various manners. In one example, as described in U.S. Pat.
No. 6,602,546, which is incorporated herein by reference, the glue 60 is
provided
within a glue tray 62 and is picked up through rotation of the applicator roll
16.
An isobar assembly 64 is mounted adjacent to the periphery of the applicator
roll
16 and removes excess adhesive from the outer peripheral surface of the
applicator roll 16 to provide an adhesive coating 4 having precise uniform
thickness on the outer peripheral surface of the applicator roll 16 after it
has
rotated past the isobar assembly 64. The isobar assembly 64 can provide
various glue thicknesses, such as at least 0.002, 0.003, 0.004, 0.005, or
0.006,
inches, or even 0.0015 inches or less.
[0037] Using this mechanism, it has been discovered that ever
thinner layers of glue film 4 on the glue applicator roll 16 can be used, and
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the bond between the flute crests and the later-applied liner is actually
improved,
despite thinner glue film 4 thickness on the applicator roll. This is achieved
by no
longer relying on glue thickness to obtain sufficient glue penetration and/or
coverage on the flute crest to ensure a good bond between the flute and the
liner
sheet.
[0038] Instead, the gap width of the nip 18 is very precisely
controlled, taking account of the flute size, to compress the flute tips 6
against
the surface of the glue applicator roll 16, with the glue film 4 on its
surface. As
shown in FIGS. 3-4, the compression of the flute crests 6 creates an
essentially
flat, conforming surface that conforms to the glue applicator roll 16 surface
contour. The rotation of that roller 16 while the flute is compressed against
it
essentially smears the very thin layer of glue film 4 over the flattened
portion of
the flute crest 6, actually `pressing' the glue 4 into the porous/fibrous
structure of
the flute crest 6.
[0039] In other words, one function of the starch adhesives in the
glue is to "bridge" or fill in the voids between two adherends, such as the
flute
crests and a face sheet. In one example, a minimum amount of glue can
correspond with the size of the hills and valleys on the adherend surfaces and
the void space between them. Indeed, the bond strength may increase with a
decreasing glue thickness. For example, the Young's modulus of the glue bond
can relatively increase with a decreasing film thickness because the glue film
becomes generally more resistant to bending as it gets thinner.
[0040] Care must be taken to ensure the degree of compression is
not sufficient to irreversibly compress the flute 7; the flute 7 must be able
to
recover or `spring back' to its original uncompressed shape following contact
with
the glue applicator roller 16. The very thin glue film 4 thickness helps
achieve
this, by not soaking the flutes 7 with liquid water, which may impede springy
recovery of the flutes 7.
[0041] In essence, the degree of compression, coupled with the
size of the flutes 7, can be used to control the thickness of the glue line
applied to
each flute crest 6. For example, glue line thickness (width in the
longitudinal
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direction for each flute 7) can be generally equal to the width of the
flattened
surface (i.e., of the flute crest 6) that is compressed against the glue
applicator
roller 16.
[0042] Using this method, it is possible to very precisely meter a
very thin glue line on the flutes 7, with finely tuned glue line thicknesses
(widths
in longitudinal flute direction) even using positioning and applicator rollers
14 and
16, and associated rotational bearings, having relatively large error
tolerances.
Because the compression-flat surface now dictates the glue line width, that
width
can be metered to a very tight tolerance despite relatively large out-of-round
tolerances for the circumferential surfaces of rollers 14, 16, or their
associated
rotational bearings.
[0043] As shown in FIG. 3, the position of the web positioning roller
14 is adjustable directly toward and away from the glue applicator roll 16
along
the direction of arrow A so that the width of the gap 18 can be precisely
adjusted
to control the degree to which the flutes 7 of the web 5 are compressed
against
the glue applicator roll 16 as they pass through gap 18. The degree of flute
compression can be controlled to a high degree of accuracy because the web
positioning roller 14 is linearly adjustable; that is, the rotational axis 32
of the web
positioning roller 14 is movable directly toward and away from the rotational
axis
31 of the glue applicator roll 16. In other words, the distance D between the
rotational axes 31, 32 can be selectively adjusted. Additionally, flexure of
the
rolls 14, 16 due to gravity does not affect the gap 18 because the gap 18 is
vertical.
[0044] The width of the gap 18 is preferably precisely closed and
opened by a closed loop control system 70. In one example, the control system
70 can include a motor and a linear transducer which moves the web positioning
roller 14 toward and away from the glue applicator roll 16 to adjust the
distance
therebetween (i.e., distance D). In another example, as shown in FIGS. 1-2, a
pair of actuators 50, such as air cylinders, hydraulic cylinders, linear
actuators, or
the like can also selectively adjust the gap between the web positioning
roller 14
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and the glue applicator roll 16 to a relatively large distance, such as about
4
inches, to meet various safety requirements.
[0045] During operation of the glue machine, the glue applicator roll
16 rotates and picks-up adhesive from the glue tray 62 onto the smooth
peripheral outer surface of the glue applicator roll 16. As the adhesive
rotates
past the isobar assembly 64, a metering rod removes excess adhesive from the
outer surface of the glue applicator roll 16 and leaves a precisely controlled
extremely thin layer of adhesive coating 4 on the outer surface of the glue
applicator roll 16. As the glue applicator roll 16 continues to rotate, the
precisely
controlled adhesive coating 4 travels from the isobar assembly 64 to a
position
adjacent the gap 18; that is, the location where the flutes 7 of the
corrugation
assembly engage the glue applicator roll 16 as previously described.
[0046] The web positioning roller 14 rotates adjacent to the glue
applicator roll 16. The rollers 14, 16 can rotate in the same direction, or
alternatively in opposite directions. The first face sheet smoothly engages
the
outer surface of the web positioning roller 14 and is held substantially
against
slippage relative thereto. As the flutes 7 of the corrugation assembly pass
through the nip point of the precisely controlled vertical gap 18 between the
glue
applicator roll 16 and the web positioning roller 14, the flutes come into
contact
with the thin coating 4 of adhesive and/or the glue applicator roll 16 as
described
above.
[0047] As the flutes 7 pass through the nip point of the vertical gap
18, the thin coating 4 of adhesive on the glue applicator roll 16 is
transferred to
the crests of the flutes 7. Any spray of adhesive generated at the nip point
is
downwardly directed without a horizontal velocity component. Therefore, no
adhesive is sprayed outside the glue tray 46, which is located directly below
the
nip point, even at high speeds. Additionally, gravity reduces or eliminates
any
pooling problems of the adhesive because gravity pulls the adhesive straight
down at the nip point.
[0048] Referring to FIG. 4, a more detailed example method for
applying adhesive to the crests of the flutes of a corrugated sheet 18 is
shown. In
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this method, the position of the web positioning roller 14 is set to adjust
the gap
18 between the web positioning roller 14 and the glue applicator roll 16 so
that
the flutes are compressed a percentage of their initial flute height upon
contact
with the glue applicator roll 16. Various degrees of compression can be
utilized,
such as 3-30, preferably 5-15 or even 5-10, percent of their initial flute
height. In
other words, the flutes are compressed down to 70-97, preferably 85-95 or 90-
95, percent of their initial flute height.
[0049] As shown, a characteristic flute 150 has a leading sloped
face 151, a trailing sloped face 152, and a crest 153. (Flute 150 in FIG. 4 is
simply a characteristic flute 7 as it passes through the gap 18. The reference
numeral 150 is used here instead of 7 merely for clarity to indicate a flute
as it
passes through the gap 18). In FIG. 4, the notation a/b/c refers to the
relative
position of the characteristic flute 150; i.e. 150a refers to a position prior
to
contact with the glue applicator roll 16, 150b refers to a position at the nip
point in
contact with the glue applicator roll 16, and 150c refers to a position
following
contact with the glue applicator roll 16. This a/b/c notation is used
consistently in
the following description with reference to FIG. 4. As the flute 150a
approaches
the glue applicator roll 16, the leading sloped face 151a first contacts the
glue
applicator roll 16 and has adhesive deposited thereupon. As the flute 150a
proceeds into full contact with the applicator roll at 150b, the leading
sloped face
151 a proceeds to 151 b as shown, with glue now having been applied both to
the
leading sloped face 151 b and the crest 153b. As can be seen from the figure,
no
glue has been applied to the trailing sloped face 152b because as the flute
proceeds from 150a to 150b, it is compressed such that the trailing sloped
face
152b is generally shielded or isolated from contact with the glue applicator
roll
16. Thus, the trailing sloped face 152b generally does not come into contact
with
any glue.
[0050] Moreover, because the passing web 5 is guided by the web
positioning roller 14, it has a generally radial contact geometry with the
glue
applicator roller 16. Thus, a relatively smaller number of flutes 150 is
generally in
contact with the glue applicator roller 16 as compared to a passing web having
a
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more straight line contact (not shown) with the glue roller. Further, the
radial
contact geometry permits the glue applicator roller 16 to contact the center
of the
crest 153b so as to localize the glue deposition. Because neither the leading
nor
trailing edges 151 b, 152b of the flute 150b are generally bonded to an
associated
face sheet, it can be beneficial to provide the glue generally upon the flute
crest
153b. As a result, the width of the glue line deposited on the crest 153b can
be
better controlled.
[0051] Because the corrugation assembly 5 is substantially
wrapped around the web positioning roller 14 and/or the size of the rider
system
is minimized, the flutes 150 contact the glue applicator roll 16 only at the
nip point
of the gap 18 so that they are wetted with adhesive and compressed at
essentially the same time. Preferably, only 1 to 2 flutes 150 are in contact
with
the adhesive and/or the applicator roll 14 at any given time. No presoaking or
post soaking of the flutes 150 occurs; that is, the flutes 150 generally do
not
touch the adhesive before reaching the nip point 18 or after leaving the nip
point
18. Therefore the dwell time, the time for which the flutes 150 are in contact
with
the adhesive and/or the applicator roll 14, is minimized so that the flutes
150 can
remain as resilient as possible.
[0052] As shown, the degree of compression is realized by the crest
153b of the flute 150b being "flattened" (or even partially concave) to
generally
conform to the outer peripheral surface of the glue applicator roller 16. That
is,
the flute 150b is generally not bent backwards or forwards. Instead, the crest
153b is compressed generally towards the web positioning roller 14. However,
because the flute 150b is generally not best backwards or forwards, the crest
153b can become generally enlarged (i.e., widened) so as to present a greater
surface area against the glue applicator roller 14. For example, the crest
153b of
flute 150b has a relatively larger surface area as compared to the crest 153a
of
flute 150a that is only partially in contact with the glue applicator roller
14, and
even the crest 153 of flute 150 that is not at all in contact with the glue
applicator
roller 14.
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[0053] In other words, the degree of compression, coupled with the
size of the flutes 150, can control the width of the flute crest 153b that is
in
contact with the glue applicator roll 16 and the glue contained thereon. As a
result, glue line width (i.e., width in the longitudinal direction for each
flute 150)
can be generally equal to the width of the flattened surface (i.e., of the
flute crest
153b) that is compressed against the glue applicator roller 16. As a result,
the
glue line width can be controlled despite changes in glue line thickness.
[0054] As the flute proceeds from 150b to 150c, initially there is
glue both on the crest 153b and the leading sloped face 151b. However, it is
generally only desired to have glue on the crest and not the leading sloped
face.
Otherwise, washboarding and directional strength variations in the finished
corrugated cardboard product can result as above described. To solve this
problem, during operation the applicator roll is rotated at a low speed such
that
the surface linear velocity of the applicator roll is much lower than the
velocity of
the corrugated sheet 5 through the gap 18. The surface linear velocity of the
glue
applicator roll 16 refers to the linear speed of the outer surface of the glue
applicator roll 16, measurable in feet per minute (or the like). The surface
linear
velocity is related to the angular velocity (i.e. rotations per minute or
RPMs) by
the relation v=2 * pi * r * S); where v is the surface linear velocity in
feet/min, r is
the radius of the glue applicator roll 16 in feet, and 12 (Omega) is the
angular
velocity of the glue applicator roll 16 in RPMs. Preferably, the outer surface
linear
velocity of the glue applicator roll 16 is less than 95% that of the
corrugated
sheet, more preferably less than 90, preferably 80, preferably 60, preferably
50,
preferably 45, and most preferably 40, percent that of the corrugated sheet
18,
though various other percentages can also be used. The above ratio of glue
applicator roll 16 speed to corrugated sheet 18 is referred to as the roll
speed
ratio.
[0055] FIG. 5 schematically illustrates an example drive system for
the glue applicator roll 16. A variable speed motor 108 can be connected to
the
glue applicator roll 16 to provide power to rotate the glue applicator roll 16
during
the operation of the machine. An electronic motor control 110 is connected to
the
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motor 108 and adjustably controls the rotational speed of the glue applicator
roll
16. This ability to control the speed of the roll 16 is an important feature
of the
present invention because it allows adjustment of the applicator roll surface
linear
velocity relative to the velocity of the web positioning roller 14 (and
therefore
corrugated sheet 5) as described above. This provides the very precise control
of
the transfer of adhesive from the glue applicator roll 16 to the flutes 7 of
the
corrugated sheet 5. In addition or alternatively, the motor controller 110 can
utilize information from a sensor 112 to control the speed of the glue
applicator
roller 16. The sensor 112 can include a glue weight sensor (e.g., as described
in
U.S. Pat. No. 6,602,546 incorporated hereinabove), a speed sensor, a flute
height sensor, a web width sensor, a web tension sensor, or even various other
types of sensors. In addition or alternatively, the motor controller 110 can
be at
least partially controlled by the closed-loop control system 70, which can
also
receive input from the sensor 112. In addition or alternatively, is to be
understood that the above-described example drive system can similarly be
applied for controlling the web positioning roller 14.
[0056] Turning briefly to FIG. 6, various glue line widths can be
utilized, and can be defined in absolute terms or, because there are numerous
standard flute sizes (i.e., A, B, C, E, F, G, etc.), as a percentage of the
total width
Wt of a single flute 150 (i.e., a percentage of the total width of a single
flute 150
of a standard flute size). In one example, it can be beneficial to have the
glue
line width Wg be generally in the range of 15-30% of the total width of a
single
flute 150. For example, each of the standard flute sizes (i.e., A, B, C, E, F,
G,
etc.) can have a preferable glue line width Wg percentage, such as 15-18%, 16-
20%, 15-19%, 19-24%, 21-27%, and 22-30%, respectively. Still, various other
percentages can also be utilized. Therefore, adjustments in gap width,
pressure
loading, and/or a radial contact geometry can provide a relatively more
consistent
amount, location, thickness, and/or width of glue that can be applied to each
flute
crest 153.
[0057] Additionally, the difference between the linear speeds of the
rollers 14, 16 can facilitate "scrubbing" of the glue 4 into the hills and
valleys on
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the flute crest 153b, which can be especially beneficial with relatively
smaller
flute sizes. In other words, the difference between linear speeds can smear
the
glue 4 into the hills and valleys on the flute crest 153b to increase wetting
and
provide an appropriate amount of glue for increased bond strength. Moreover,
the pressure at which the flutes 7 are compressed against the roller 16
surface
(and the corresponding degree of compression of those flutes 7) can also
facilitate the "scrubbing" of the glue 4 into the hills and valleys on the
flute crest
153b. However, it can also be beneficial to control the speed differential
and/or
the pressure applied to the flutes 7 so as to obtain the desired scrubbing
action
without causing damage to the web 5.
[0058] In addition to the relative linear speeds of the rollers 14, 16,
various other factors can influence the glue deposition upon the flutes 7. For
example, the width of the gap 18 (i.e., as determined by the width D between
the
rotational axes 31, 32 of the rollers 14,16) and/or the pressure applied
between
the flutes 7 and the glue applicator roller 16 can also influence the glue
deposition.
[0059] In one example, as shown in FIGS. 1-2, an actuator 50,
which can act as a pressure and/or gap metering controller, can be utilized to
control the width of the gap 18 and/or the pressure applied to the flutes 150.
The
actuator 50 can be coupled to the second support arm 20b, for example, which
otherwise is freely adjustable during machine operation as described
previously
herein. The controller 50 is capable of precisely metering the width of the
gap 18
between the positioning and applicator rollers 14 and 16, and/or the pressure
exerted by the roller 14 on the flutes against the applicator roller 16 to
achieve
optimal glue application to the passing flute crests 6. Because of the cross-
member 25, the actuator 50 does not have to compensate or account for tension
in the web 5, nor is its operation or the precise metering of gap 18
substantially
disturbed or affected due to even significant sudden or unpredictable changes
in
web tension. This presents several significant advantages over conventional
glue
machines. First, the actuator 50 can incorporate very high precision motors,
servos, pneumatic cylinders, or the like, or suitable combinations of these or
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other conventional mechanical or pneumatic or hydraulic metering devices, to
achieve very high precision metering of the position of roller 14 as well as
the
pressure exerted thereby on the web 5 against the applicator roller 16, to
provide
precise dynamic gap metering control for a wide range of different flute sizes
(e.g., sizes A through E or smaller) to achieve optimal glue-to-flute
application.
Conventionally, very high precision metering components for the controller 50
were problematic due to relatively large web tension-effect forces, as well as
sudden significant changes in such forces, that the controller 50 had to
withstand
and compensate for. Because these large magnitude forces have been
mechanically nulled or compensated out by the cross-member 25, higher
precision and more sensitive metering devices can be used in the actuator 50.
Optionally, the actuator 50 can be coupled to the first support arm 20a in
order to
regulate the width of the gap 18, though this is less preferred.
[0060] Thus, the roller 14 is permitted to float freely within a
predetermined range in an arc about its support pivot joint 22b during
operation
of the glue machine. Thus, the roller 14 is freely adjustable within this
predetermined range during operation of the glue machine. That predetermined
range may vary based on the machine and its particular application, but
generally
will be broad enough to accommodate a wide range of flute sizes, as well as a
broad range of compression rates for each flute size that is to be compatible
with
the glue machine. The predetermined range can be, for example, an arc length
of
up to at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, inches, with the controller 50
capable
to maintain precise dynamic gap metering control within such range.
[0061] The glue machine according to the invention allows very
precise metering of the gap 18 regardless and independent of the web tension,
or of sudden changes in the web tension based on external factors beyond the
scope of the glue machine. As described herein, it is important to accurately
meter the width of the gap 18 and the pressure exerted by the positioning
roller
14 against the flutes 7 (against applicator roller 16) to ensure the correct
amount
of glue is applied across different flute sizes when such different sizes are
used.
This is especially important when changing flute sizes in the glue machine.
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[0062] However, because the glue machine is a dynamic system, it
can be beneficial to utilize a control system 70 to maintain a desired gap 18
and/or the pressure exerted against the flutes 7. In addition or
alternatively, the
control system can be utilized to maintain the rollers 14, 16 parallel to each
other
to ensure a consistent gap 18 and/or pressure application along the length of
the
rollers 14, 16.
[0063] As previously noted, the gap 18 is preferably precisely
closed and opened by the control system 70. Though described herein as a
closed-loop control system, an open-loop control system can also be utilized.
In
one example, the control system 70 can include one or more motors and linear
transducer(s) which move the web positioning roller 14 toward and away from
the
glue applicator roll 16. In another example, as shown in FIGS. 1-2, a pair of
the
actuators 50, such as air cylinders, hydraulic cylinders, linear actuators, or
the
like can also selectively adjust the gap between the web positioning roller 14
and
the glue applicator roll 16. Still, more than two actuators can also be used.
[0064] Side to side accuracy of the precise gap 18, that is along the
length of the web positioning roller 14, can be controlled in various manners.
In
one example, side to side accuracy can be maintained with two adjustment jacks
and a cross-connecting shaft. The shaft transversely extends the length of the
web positioning roller 14 and the adjustment jacks are located at or near the
ends of the shaft so that the web positioning roll outer surface can be
adjusted to
be parallel to the applicator roll outer surface. It is noted, however, that
the cross-
connecting shaft could alternately be a central shaft in the web positioning
roller
14. Still, because the glue machine is a dynamic system during operation, the
rollers 14, 16 can become skewed to varying degrees due to varying web
tension, flute height, mechanical tolerances, etc.
[0065] In another example, as shown in FIGS. 7A-7B, the control
system 70 can selectively and independently adjust either or both of the
actuators 50a, 50b, based upon a comparison of a plurality of measurements of
the width of the gap 18, to maintain the web positioning roller 14 outer
surface to
be precisely parallel to the glue applicator roll 16 outer surface. Each of
the pair
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of actuators 50a, 50b has a control arm 52a, 52b coupled (directly or
indirectly) to
each side of the web positioning roller 14. As a result, independent
adjustment
of the control arms 52a, 52b along the direction of arrow B can create a
virtual
pivot point 72 for the web positioning rollers 14 generally about the
centerline of
the roller 14. Though the control system 70 will be described with reference
to
making adjustments to the web positioning roller 14, it is to be appreciated
that
the control system can also be adapted to make adjustments to the applicator
roller 16 (e.g., in addition to, or as an alternative to, the roller 14).
[0066] For example, as shown in FIG. 7A, the web positioning roller
14 is arranged generally parallel to the applicator roller 16. The rotational
axes
31, 32 of the rollers 14, 16 are substantially parallel, such that the
distance Dl
between the axes 31, 32 on the left-hand side is substantially equal to the
distance D2 on the right-hand side. As a result, the width of the gaps 18a,
18b
located on each side of the roller 14 are substantially equal, and a web 5
passing
therethrough can experience substantially the same gap and/or pressure along
the lengths of the rollers 14, 16.
[0067] However, turning to FIG. 7B, the rotational axes 31, 32 of the
rollers 14, 16 are illustrated skewed with respect to each other. It is to be
understood that similar numbers are used for similar elements, and are labeled
with a prime (') designation. As shown, the web positioning roller 14' is
skewed
relative to the applicator roller 16 about the virtual pivot point 72'. The
distance
D3 is less than the distance D4, and as a result the width of gap 18a' is less
than
the width of gap 18b'. Thus, a web 5 passing therethrough will experience a
relatively smaller gap (and possibly a higher pressure) located along the left-
hand side relative to the relatively larger gap (and possibly a lower
pressure)
located along the right-hand side. As a result, glue line width and/or
thickness
can undesirably vary, and/or the flutes 7 can become damaged.
[0068] Because the glue machine is a dynamic system during
operation, the rotational axes 31, 32 of the rollers 14, 16 can become skewed
to
varying degrees for various reasons. Thus, the control system 70 can be
utilized
to automatically maintain each of the rotational axes 31, 32 to be
substantially
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parallel to one another in real time, which will maintain the width of the
gaps 18a,
18b located on each side of the roller 14 to be substantially equal. To
accomplish this, the control system 70 can employ a control algorithm 80, such
as the one illustrated in FIGS. 8A-8B. The control algorithm 80 can be
performed
by a computer or the like, such as a programmable logic controller (PLC),
though
the algorithm 80 can also be performed by various other computers, digital, or
even analog components. Moreover, some or all of the control algorithm 80 can
be performed by digital or analog circuitry. Similarly, inputs provided to the
control system 70, such as various inputs to the control algorithm 80, can be
provided in digital and/or analog formats. Some or all of the steps of the
algorithm 80 can be automated, and/or some of the steps of the algorithm 80
can
be provided manually by an operator, such as various input values or the like.
Moreover, the control algorithm 80 can include more, less, and/or even
different
steps than those illustrated herein.
[0069] Turning now to FIG. 8A, the control algorithm 80 will be
described in further detail. First, in step 81, a desired width of the gap 18
is set
between the web positioning roller 14 and the glue applicator roller 16 to
thereby
regulate a degree of compression of the flutes 7 against the applicator roller
16.
The desired width of the gap 18 can be manually input (directly or
indirectly), or
automatically selected. For example, an operator can manually input a flute
size,
and the control system 70 can select a desired width of the gap 18 that is
associated with each of the standard flute sizes (e.g., sizes A through E or
smaller), such as from a discrete set of gap widths or even by calculation of
a
gap width. In one alternative, an operator can either manually input a gap
width
directly (i.e., in inches, millimeters, etc.). In another alternative, the
control
system 70 can include an automatic flute sensor, such as that described more
fully herein below in association with FIGS. 9-10, that can automatically
determine the standard flute size, and choose a desired gap width. Upon
determining the desired gap width, the control system 70 can utilize the
actuators
50a, 50b to provide the desired and predetermined gap width between the web
positioning roller 14 and the glue roller 16 on each side thereof.
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[0070] Next, at step 82, a desired glue machine loading is set
between the web positioning roller 14 and the glue applicator roller 16. The
desired glue machine loading can be determined in terms of pounds per lineal
inch (PLI), though various other units can also be used. Generally, the glue
machine loading value can be within the range of 1 - 10 pounds, though various
other values can also be used. In other words, the glue machine loading
determines the amount of force the actuators 50a, 50b will apply to the flutes
7
against the glue applicator roller 16. It is to be understood that the total
force
applied to the flutes 7 will be generally equivalent to the sum of the forces
provided by each of the actuators 50a, 50b. For example, if each of the
actuators 50a, 50b provides 50 pounds of force, the flutes will experience a
total
force of 100 pounds. Again, the glue machine loading can be manually input
(directly or indirectly), or automatically determined by the control system
70.
[0071] Next, at step 83, the width of the web 5 is determined. The
width of the web 5 refers to be the transverse width of the web 5 (i.e., the
dimension oriented transverse to the longitudinal axis of the web 5). As shown
in
step 84, the width of the web 5 can be automatically determined (step 85a) by
the control system 70, or manually input (step 85b, directly or indirectly).
An
automatic web width sensor can be a contact or non-contact design, such as a
mechanical feeler, a light curtain or the like for measuring the width, etc.
Upon
determining the web width, the algorithm 80 proceeds in step 86 to store the
width value, such as in a variable Wl.
[0072] Next, at step 87, the loading pressure for the actuators 50a,
50b is calculated. The loading pressure is based upon the glue machine loading
and the web width. As described above, the glue machine loading can be
provided in units of pounds per lineal inch, while the web width can be
provided
in units of lineal inch. Thus, upon multiplying these two values together, the
loading pressure can be provided in units of pounds (force). For example,
where
the glue machine loading is 2 pounds per lineal inch, and the web width is
determined to be 50 inches, then the loading pressure is calculated to be 100
pounds force (i.e., 2 x 50 = 100). As a result, the sum of the forces provided
by
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the actuators 50a, 50b would be 100 pounds force. Generally, each of the
actuators may provide approximately half of the loading pressure (i.e., 50
pounds
each), though the actual amount provided by each of the actuators 50a, 50b may
vary and/or be unequal during operation. Moreover, in step 88, the algorithm
80
can calculate and transmit the appropriate signals or values 01 and Dl for
each
of the actuators 50a, 50b, respectively, to directly or indirectly obtain the
desired
loading pressure.
[0073] Next, in step 89, the distances between the web positioning
roller 14 and the glue applicator roller 16 are measured on each side (i.e.,
18a
and 18b of FIG. 7A) of the rollers 14, 16. For example, in step 90, a first
actual
width of the gap 18a between the first end of the web roller 14 and the glue
roller
16 is measured. The first actual width is stored by the algorithm 80 as value
PTO1. Similarly, in step 91, a second actual width of the gap 18b between the
second end of the web roller 14 and the glue roller 16 is measured. The second
actual width is stored by the algorithm 80 as value PTD1. It is to be
understood
that the first and second actual widths can be measured in various manners. In
one example, the actual gap widths can be measured via a sensor, such as a
position transducer, coupled to or incorporated into each of the actuators
50a,
50b. In another example, the actual gap widths can be measured via a sensor
that measures the distance (e.g., distances D1-D4 of FIGS. 7A-7B) between the
rotational axes 31, 32 of the rollers 14, 16 and calculates the gaps 18a, 18b.
In
yet other example, the actual gap widths can be directly measured between the
rollers 14, 16, such as through various contact or non-contact mechanical,
electronic, or optical means. Various examples can include mechanical feelers,
photodetectors, lasers, radar and/or ultrasonic sensors or the like.
[0074] Next, in step 92, the actual gap widths PTO1 and PTD1 are
compared against each other. In one example, the algorithm 80 can merely
determine which of the values is greater than the other, while in another
example, the algorithm 80 can determine a percentage difference. In another
example, the algorithm 80 can calculate a difference distance between the
actual
gap widths PTO1 and PTD1 (i.e., PTO1 - PTD1). Next, in step 93, the algorithm
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80 can determine how to independently operate the actuators 50a, 50b to reduce
the difference between the actual gap widths. Generally, at step 93, the
algorithm 80 will increase the length of the control arm 52a, 52b associated
with
the relatively larger actual gap width, while maintaining or even decreasing
the
length of the control arm 52a, 52b associated with the relatively smaller
actual
gap width. Though length adjustment to both of the control arms 52a, 52b have
been discussed, it is to be understood that corrections can be applied to only
one
of the control arms 52a, 52b while the other remains stationary.
[0075] For example, where the actual gap width PTO1 is
determined to be larger than PTD1, the algorithm 80 will proceed to step 94.
The
algorithm 80 will calculate new values for each of the actuators 50a, 50b. For
example, because the gap width PTO1 is determined to be larger than PTD1, the
algorithm 80 can subtract a value, such as an error signal, from the original
signal 01 provided to the actuator 50a in step 88 to provide an adjustment
distance therefor. Similarly, the algorithm 80 can add a value, such as the
error
signal, to the original signal Dl provided to the actuator 50b in step 88 to
similarly
provide an adjustment distance therefor. In other words, because the gap width
PTO1 is larger, the control arm 52a of the associated actuator 50a is extended
an adjustment distance, while the control arm 52b of the associated actuator
50b
is retracted an adjustment distance. Various error signals can be used to
generate various adjustment distances. In the shown example, because the
virtual pivot point 72 is located generally about the center of the web
positioning
roller 14, the error signal can be equal to one-half of the difference between
the
actual gap widths PTO1 and PTD1. Still, the error signals can be different,
non-
equal, etc.
[0076] The algorithm can then store the new calculated actuator
signals (e.g., adjustment distances) as values 02 and D2. Next, in step 97,
the
algorithm 80 can transmit the appropriate corrected signals or values 02 and
D2
for each of the actuators 50a, 50b, respectively, to directly or indirectly
obtain the
corrected loading pressure for adjustment of the control arms 52a, 52b to
offset
the skewed alignment between the rollers 14, 16. It is to be understood that
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while the loading pressures for each of the actuators 50a, 50b may increase or
decrease, and/or may be un-equal, the sum of the forces provided by the
actuators 50a, 50b would remain as previously calculated in step 87 (e.g., 100
pounds force in the described example).
[0077] Next, in step 98, the algorithm 80 will proceed to measure
and determine the effect of the changes applied to the actuators 50a, 50b. As
shown, the algorithm 80 will loop back to steps 90 and 91 to re-measure the
actual gap widths 18a, 18b as described previously herein. The algorithm 80
will
then proceed through steps 92-98 to make further corrections. It is to be
understood that the algorithm 80 can repetitively proceed through steps 89-98
in
an iterative fashion until the actual measured gap widths PTO1 and PTD1 are
substantially equal. Still, even where the measured gap widths are
substantially
equal, the algorithm 80 can still continue to perform steps 89-98 iteratively
during
operation of the glue machine 10 because of the dynamic nature of its
operation.
[0078] In addition or alternatively, the control system 70 can utilize
threshold values to reduce, such as prevent, correction of de minimis
differences
between the actual gap widths 18a, 18b. For example, the sensors for
measuring the actual gap widths 18a, 18b can have a resolution, such as 32,000
units or counts. Each unit or count can correspond to a known value, such as
0.001 inches or the like. The control algorithm 80 can be selectively set to
ignore
de minimis differences between the actual gap widths 18a, 18b based upon a
threshold number of units. For example, the threshold can be 10 units or
counts,
though various other threshold values can be programmed into the algorithm 80.
In other words, the control algorithm 80 can ignore any de minimis difference
between the actual, measured gap widths PTO1 and PTD1 that is less than 10
units of sensor resolution.
[0079] Turning briefly back to step 95, it is to be understood that
this step operates similarly and alternatively to that of previously described
step
94 to calculate new values for each of the actuators 50a, 50b. That is, where
the
gap width PTO1 is determined to be less than PTD1 (e.g., see FIG. 7B), the
algorithm 80 can add a value, such as an error signal, to the original signal
01 to
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provide an adjustment distance therefor. Similarly, the algorithm 80 can
substract a value, such as the error signal, from the original signal Dl to
similarly
provide an adjustment distance therefor. In other words, because the gap width
PTO1 is smaller, the control arm 52a of the associated actuator 50a is
retracted
an adjustment distance, while the control arm 52b of the associated actuator
50b
is extended an adjustment distance. The algorithm can then store the new
calculated actuator signals (e.g., adjustment distances) as values 02 and D2,
and in step 97, can transmit the appropriate corrected signals or values 02
and
D2 for each of the actuators 50a, 50b. The algorithm 80 can then proceed to
step 98 to loop back to step 89 to repeat the process, as described previously
herein.
[0080] Similarly, turning briefly back to step 96, it is to be
understood that this step operates similarly and alternatively to both of
previously
described steps 94 and 95 to calculate new values for each of the actuators
50a,
50b. That is, where the gap width PTO1 is determined to be substantially equal
to PTD1 (e.g., see FIG. 7A), or even within the previously described sensor
resolution threshold, the algorithm 80 can maintain the values for each of the
control arms 52a, 52b. The algorithm 80 can pass, such as copy, the values 01
and Dl to provide the new values 02 and D2. Alternatively, if desired, the
algorithm 80 can add a value, such as zero, to each of the original signals 01
and Dl to provide the new values 02 and D2. The algorithm 80 can then
proceed to step 98 to loop back to step 89 to repeat the process, as described
previously herein.
[0081] It is to be understood that in addition to maintaining the
rollers 14, 16 parallel to each other, the control system 70 can also be
utilized to
ensure a consistent gap 18 along the length of the rollers 14, 16. For
example,
as previously described, the algorithm 80 can similarly begin at step 81 to
determine a desired width of the gap 18. The gap 18 can be manually or
automatically selected, and can be directly input in absolute terms (i.e., in
inches
or millimeters), or can be selected from a discrete set of width values that
are
each associated with the standard flute sizes (e.g., sizes A through E or
smaller).
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Next, the algorithm 80 can proceed through steps 82-88 as described above to
move the web positioning roller 14 to set the initial, desired gap width. The
algorithm 80 may further include a step of verifying, either manually or
automatically, the actual gap distance. Next, the algorithm 80 can them
proceed
repetitively and iteratively through steps 89-98 to automatically adjust the
position
of the web positioning roller 14 relative to the glue applicator roller 14,
via
adjustments of the control arms 52a, 52b, to maintain the preselected and
desired width of the gap 18 along the lengths of the rollers 14, 16. In other
words, once the initial gap 18 is set, the algorithm 80 can maintain the
preselected width along the lengths of the rollers 14, 16 via constant
comparison
of the measured actual gap widths PTO1 and PTD1 and selective adjustment
thereof. Still, more or less various other measurements can also be utilized.
[0082] In addition or alternatively, the control system 70 can also be
utilized to ensure a consistent pressure application along the length of the
rollers
14, 16. For example, as previously described, the algorithm 80 can similarly
begin at step 81 to determine a desired width of the gap 18 via manual or
automatic means. Next, the algorithm 80 can proceed through steps 82-88 as
described above to move the web positioning roller 14 to set the initial,
desired
gap width, and also the desired loading pressure. The algorithm 80 may further
include a step of verifying, either manually or automatically, the actual gap
width
and/or the loading pressure applied. Next, the algorithm 80 can them proceed
repetitively and iteratively through steps 89-98 to automatically adjust the
position
of the web positioning roller 14 relative to the glue applicator roller 14,
via
adjustments of the control arms 52a, 52b, to maintain the preselected and
desired loading pressure along the lengths of the rollers 14, 16. In other
words,
once the initial loading pressure is set, the algorithm 80 can maintain the
preselected pressure along the lengths of the rollers 14, 16 via constant
comparison of the measured actual gap widths PTO1 and PTD1 and selective
adjustment thereof. Still, the algorithm 80 can include various additional
steps to
measure, verify, and/or adjust the actual pressure applied along the lengths
of
the rollers 14, 16 via adjustment of the control arms 52a, 52b. For example,
the
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algorithm 80 can include a set of steps similar to those of steps 89-98 that
are
performed repetitively and iteratively to compare the actual pressure applied
by
each of the actuators 50a, 50b, and to adjust the pressures thereof until the
difference between the actual pressures is substantially zero (or even within
the
previously described sensor resolution threshold). Still, the total force
applied to
the flutes 7, will be generally equivalent to the sum of the forces provided
by
each of the actuators 50a, 50b via the loading pressures thereof.
[0083] In addition or alternatively, as indicated in the above
description, the desired width of the gap 18 can be automatically determined
in
step 81 for use in some or all of steps 82-88. Thus, the control system 70 can
include an automatic flute sensor that can automatically determine the flute
size.
Where the flute size corresponds to a standard flute size (e.g., sizes A
through E
or smaller), the algorithm 80 can determine a desired gap width from among a
discrete set of predetermined and associated gap widths. Alternatively, even
if
the flute size corresponds to a standard flute size, the algorithm 80 can
determine, such as calculate, a desired gap width based upon the actual
measured flute size. In either event, the algorithm 80 can determine a desired
gap width based upon the measurement of a single flute, or even a plurality of
flutes. In one example, the algorithm 80 can determine an average flute height
based upon a measurement of a plurality of flute heights. In another example,
the algorithm 80 can determine the flute height based upon a minimum,
maximum, median, or mode value of a plurality of flute heights.
[0084] The automatic flute height sensor can be a non-contact
design, such as a light curtain or the like (see FIG. 9), or a contact design,
such
as parallel rollers (see FIG. 10), for measuring the flute height. Upon
determining
the flute height and then the desired gap width, the control system 70 can
utilize
the actuators 50a, 50b to provide the desired and predetermined gap width
between the web positioning roller 14 and the glue roller 16 on each side
thereof.
Though the automatic flute height sensor can be located variously about the
glue
machine 10 (or even at various other locations in the corrugation
manufacturing
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process), it can be beneficial to locate the automatic flute height sensor
upsteam
of the glue applicator roller 16 to permit advance adjustment of the gap
width.
[0085] Turning now to FIG. 9, one example of a non-contact
automatic flute height sensor 170 is described. A portion of the corrugated
web
5, including flutes 7 having a flute height, is driven though the non-contact
automatic flute sensor 170 by an idler roller 171 or the like. As shown, the
non-
contact automatic sensor 170 can be a light curtain or the like that includes
a pair
of light towers 172, 174 separated by a distance for optically measuring the
average height of the flute crests.
[0086] A photoelectric transmitter is contained within either or both
of the light towers 172, 174 and projects an array of synchronized, parallel
infrared light beams 176 to a receiver unit (i.e., the other of the light
towers 172,
174). When an opaque object, such as the tips of the flutes 7, interrupts one
or
more of the light beams 176, such as beam 178, control logic of the light
curtain
sends a signal to the control system 70. In one example, the photoelectric
transmitter unit can contain light emitting diodes (LEDs) that emit pulses of
visible
light, or invisible infrared or ultraviolet light, when energized by the light
curtain's
timing and logic circuitry. The light pulses can be sequenced (i.e., one LED
is
energized after another), and/or modulated (i.e., pulsed at a specific
frequency).
For example, corresponding photo-transistors and supporting circuitry in the
receiving unit can be designed to detect only the specific pulse and frequency
designated for it to offer enhanced usability and/or rejection of external
light
sources. The control logic, user controls and diagnostic indicators may be
self-
contained, or even a portion of the control system 70.
[0087] Thus, by determining which of the light beams 176 in the
array were interrupted by the passing flutes 7, the control system 70 can
determine the height of the flutes 7. Similarly, if the passing flutes 7
interrupt
multiple, different light beams 176, the control system 70 can determine an
average flute height based upon which light beams 176 were interrupted.
Moreover, it is to be understood that the resolution of the light curtain,
that is, the
number and/or density of light beams 176 available for interaction with the
flutes
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7, can vary and can determine the accuracy of the non-contact automatic flute
height sensor 170.
[0088] In another example, the photoelectric transmitter unit can
contain lasers that emit pulses of visible or invisible light when energized
by the
light curtain's timing and logic circuitry. The light pulses can be sequenced
(i.e.,
one laser is energized after another), and/or modulated (i.e., pulsed at a
specific
frequency), and can otherwise operate as discussed above. In yet other
examples, the non-contact automatic flute height sensor 170 can utilize radar
or
ultrasonic sensors or the like.
[0089] In addition or alternatively, the non-contact automatic flute
height sensor 170 can utilize one or more movable sensors. For example, either
or both of the light towers 172, 174 can include a movable light sensor 179
that is
vertically movable with respect to the light towers 172, 174. The movable
light
sensor 179 can utilize LEDs, lasers, or the like as described above. The
receiving light tower 174 can include a plurality of receiving sensors or
photodetectors, or can even include a matching vertically movable sensor that
moves in unison with the sensor 179. In one example operation, the movable
light sensor 179 can emit a light beam (similar to light beams 176) while it
vertically descends in a downwardly fashion until the light beam is
interrupted by
a passing flute 7. As a result, the height of the flutes 7 can be inferred
from the
vertical position of the movable sensor 179, or even the particular receiving
sensor or photodector to last receive a signal.
[0090] Turning now to FIG. 10, one example of a contact automatic
flute height sensor 180 is described to mechanically measure the average flute
height. A portion of the corrugated web 5, including flutes 7 having a flute
height,
are driven though the contact automatic flute sensor 180 by a first roller 182
or
the like. As shown, the contact automatic flute sensor 180 can be pair of
counter-rotating rollers 182, 184 that measure the difference in instantaneous
linear speeds to determine the average height of the flute crests.
[0091] The first roller 182 is rotated in a first direction at a fixed
angular velocity and carries the web therewith. The two rollers 182, 184 are
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located sufficiently close together such that a portion of the flutes contact
the
second roller 184 (i.e., an idler roller) and cause it to rotate (e.g.,
similar to two
mated spur gears). The second roller 184 rotates in the opposite direction at
generally the same angular velocity. The second roller 184 may include
corrugation or other surface features or geometry to facilitate rotation by
the
passing flutes 7, or may be sufficiently close to the first roller 182 such
that
frictional drag of the passing flutes 7 causes rotation.
[0092] The rollers 182, 184 can have various radii. However, for
simplicity, each of the rollers 182, 184 in this example can have the same
radius,
R, and R3, respectively. A portion of the corrugated web 5, including flutes 7
having a flute height, is driven by rotation of the first roller 182. Thus,
the
effective outer radius R2 of the first roller is equal to the sum of the
radius of the
roller and the flute height (i.e., R, + the flute height).
[0093] Next, the instantaneous linear speeds (ILS) of the first and
second rollers 182, 184 are measured by suitable speed sensors 186, 188 and
the data transmitted to the control system 70. The instantaneous linear speed
of
the first roller 182 is measured about a portion that includes the passing
flutes 7
(i.e., about a portion defined by R2). The control system 70 can then
determine
the average flute height based upon a comparison of the measured
instantaneous linear speeds ILS1, ILS2 of the rollers 182, 184, respectively.
[0094] For example, the instantaneous linear speed of the first roller
182 can be calculated as the circumference (2 * pi * effective radius)
multiplied
by the angular velocity (RPM,). The effective radius, as described above, is
equal to the sum of the known radius of the first roller 182 and the unknown
flute
height (i.e., R, plus the flute height). Thus, the instantaneous linear speed
ILS,
of the first roller 182 can be expressed as (2 * pi * (Ri + flute height)) *
RPM,.
Similarly, the instantaneous linear speed ILS2 of the second roller can be
calculated as the circumference (2 * pi * radius R3) multiplied by the same
known
angular velocity, RPM,. In other words, the two resultant equations can be re-
written to be RPM, = (ILS, / (2 * pi * (Ri + flute height)) and RPM, = (ILS2 /
(2 * pi
~
3=
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[0095] As a result, the common variables (2 * pi) can cancel out and
the only unknown between the two equations is the flute height. Therefore, the
flute height can be determined by cross-multiplying the two equations to
arrive at
the final equation of (ILS, /(ILS2) =((Ri + flute height) /(R3)), from which
the flute
height can be easily calculated. Moreover, to obtain an average flute height,
multiple samples of each of the instantaneous linear speeds ILS1, ILS2 can be
measured and multiple flute heights calculated and averaged out.
[0096] Still, various other contact automatic flute height sensors can
be used. For example, an arm (not shown) can ride upon the flute crests and
displacement of the arm (i.e., vertical or angular displacement) can be
measured
as the flute pass thereby to determine the flute height. The arm can be
resiliently
displaced against the flutes, or can be held by gravity.
[0097] It is to be noted that precise gap metering control has been
described above with respect to adjusting the position of the web positioning
roller 14. Alternatively, it is contemplated that gap metering control can be
achieved by fixing the position of the positioning roller 14 and adjusting the
position of the glue roller 16. This construction, however, is less preferred
because of the relative complexity associated with adjusting the position of
the
glue applicator roller 16 during machine operation. For example, the thickness
of
the glue film 4 applied to the circumferential surface of the applicator
roller 16
also typically is precisely metered to achieve optimal glue application, e.g.,
by the
methods described in U.S. Pat. No. 6,602,546 incorporated hereinabove. Thus,
in order to adjust the relative position of the applicator roller 16, the
relative
positions of a substantial number of additional machine components also would
need to be correspondingly adjusted, such as the glue tray and isobar
assemblies described in that patent. For example, one method would be to
incorporate all of the applicator roller-associated components onto a
subassembly and to provide a rail system for translating the subassembly
relative
to the positioning roller 14. However, adjustment in this manner may
compromise
the precision of the glue film application components, as well as contribute
excessive complexity and cost to the machine's manufacture. For at least these
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reasons, it is preferred to adjust the position of the positioning roller 14
relative to
that of the applicator roller 16 whose position is fixed on a stationary
rotational
axis, and to mechanically cancel out web tension-induced forces acting on the
positioning roller, or on any of its associated linkages, by incorporating a
web
tension nulling mechanism as disclosed herein.
[0098] The invention has been described with reference to the
example embodiments described above. Modifications and alterations will occur
to others upon a reading and understanding of this specification. Examples
embodiments incorporating one or more aspects of the invention are intended to
include all such modifications and alterations insofar as they come within the
scope of the appended claims.
34
